The invention relates to an improved multichannel magnetic transducer structure having a multiple leg back core and to a method of making the improved transducer structure. More particularly, the invention relates to an improvement in the rear leg of the multiple leg core structure and in the associated transducing windings, respectively.
Multiple leg magnetic transducers are known, for example, from the U.S. Pat. Nos. 3,881,194 and 4,293,884 both assigned to Ampex Corporation, assignee of this patent application, which patents are hereby incorporated by reference.
The U.S. Pat. No. 3,881,194 describes a multiple leg magnetic transducer having back core legs contiguous with the pole pieces and each leg defining a separate flux path. A transducer with two legs is described, one leg carrying a low impedance record winding and the other leg a high impedance playback winding, also referred to as reproduce winding. The transducer operates in either recording or reproducing mode. The switching between modes is accomplished by electromagnetically blocking that leg which is not used in a particular mode so that no appreciable magnetic signal flux passes through that leg.
The U.S. Pat. No. 4,293,884 describes a multiple leg magnetic transducer of the type described in U.S. Pat. No. 3,881,194. More particularly a transducer structure is described whose back core has an intermediate leg and a rear leg extending substantially in parallel with the intermediate leg. Both legs are contiguous with the pole pieces and each leg defines a separate magnetic flux path. A recording coil is placed on the intermediate leg while a reproducing coil is placed on the rear leg. Depending on the particular operation mode one of these legs is electromagnetically gated to prevent passage of magnetic flux therethrough while the other leg is in operation.
The U.S. Pat. No. 4,293,884 further discloses a particular structure for supporting the multiple leg transducer to eliminate undesirable spacing between the corresponding intermediate and rear leg portions, respectively. A simplified cross sectional view of that prior art transducer is shown in FIG. 1 of the attached drawings and will be briefly discussed below. The transducer 11 of FIG. 1 has two corresponding core portions 12, 14 supported by side pieces 70, 72, respectively. A transducing gap 20 is formed between abutting end faces 24, 26 of corresponding magnetic poles 48, 52. The core portions 12, 14 are assembled with corresponding poles 48, 52 and leg portions 28, 54; 30, 56 in registration and with corresponding end faces 24, 26; 32, 34 and 36,38 abutting. The thusly assembled core portions and side pieces are bonded together under pressure by a suitable bonding material 90 in a known manner. It is noted that showing of the bonding material 90 is deleted from inner spaces between the core portions for better clarity of representation. The U.S. Pat. No. 4,293,884 further describes recording coils placed on intermediate legs 28, 54 and reproducing coils on rear legs 30, 56 (coils are not shown in FIG. 1). The transducing coils are first prewound away from the core and subsequently inserted on the core prior to assembling the corresponding core portions together. These coils are prewound on a self-supporting insulating bobbin whose perimeter is larger than that of the underlying core to facilitate transfer on the core. For the latter reason the coil receiving cores are known to be tapered as it is shown in FIG. 1. Consequently, the prewound coils inherently occupy excessive space thereby reducing the number of windings which can be accomodated due to limited lateral space between adjacent channels. The magnetic coupling between the coil and associated core portion is substantially reduced due to the loose fit of the coil, thus producing undesirable leakage flux.
When utilizing the known multichannel multiple leg transducers such as described in the U.S. Pat. No. 4,293,884, in high density recording and reproducing applications having closely spaced adjacent channels, undesirable channel-to-channel crosstalk may result between adjacent channels. In certain applications, for example when one channel of the multichannel transducer is in the recording mode and an immediately adjacent closely spaced channel is in the reproducing mode, a substantial amount of leakage flux from the recording coil may be induced in the reproducing coil of the adjacent channel. In some applications such as professional audio recording and reproduction the above-indicated crosstalk may exceed acceptable limits.
Further shortcomings of the above-indicated prior art multichannel multileg transducers are that when utilized for high channel densities it has been a known practice to mechanically compress the prewound coils after placing them on the core to reduce their size in the channel-to-channel direction. Applying mechanical force to the coils in the above manner often resulted in damaging the small diameter wire which thus became interrupted or alternatively grounded or a number of windings became shorted within the coil. A high rejection rate resulted.